The present invention generally relates to a liquid material dispensing apparatus and methods and, more specifically, to apparatus and methods for monitoring the quality-of the application of patterned viscous material onto moving strands.
In various types of manufacturing operations, it is necessary to bond narrow substrates, such as thin elastic strands, with a wider substrate, such as one or more sheets of material. Fiberized adhesives, including temperature and/or pressure sensitive adhesives, are commonly dispensed onto woven and nonwoven flat substrates and stretched elastic strands during the manufacture of hygienic articles, such as diapers, incontinence pads and other absorbent undergarments. For manufacturing such hygienic articles, small volumes of adhesive may be dispensed onto one or more individual elastic strands simultaneously, either before or after the strand has been laid against a substrate, to bond each strand to the substrate. In this manner, overlapping portions of the same material may be bonded together with stretched elastic strands secured therebetween or two distinctly different substrates may be bonded together as a laminate with stretched elastic strands secured therebetween. This is a popular manufacturing technique for elasticizing specific areas of hygienic articles, such as the waistbands, leg cuffs, and standing leg gathers of diapers and adult incontinence products.
One type of coating applicator or adhesive dispenser that has been used extensively for bonding one or more elastic strands to one or more flat substrates is CONTROLLED FIBERIZATION(trademark) (CF(trademark)) technology, which is described, for example, in U.S. Pat. No. 4,785,996. This familiar adhesive dispensing technique impacts a dispensed continuous filament of adhesive with air jets to impart a swirl to the adhesive filament transverse to the direction of movement of a strand receiving the adhesive filament. In this manner or a similar manner, the continuous adhesive filament may be dispensed in any pattern onto an individual elastic strand while the strand is moving and separated from the substrate. The adhesive filament wraps itself around each elastic strand before the strand contacts the substrate, which strengthens the adhesive bond between the elastic strand and substrate. Other conventional adhesive filament dispensing techniques and apparatus have been employed for producing patterns of adhesive on an elastic strand, such as vascillating patterns disclosed in U.S. Pat. No. 6,077,375 and omega-shaped patterns as disclosed in U.S. Pat. Nos. 6,461,430, 6,200,635 and 6,197,406.
Another adhesive dispensing technique for securing elastic strands to a substrate relies upon dispensing discrete areas of an adhesive onto moving strands while the strands are separated from the substrate. For example, the discrete areas may define a repeating pattern consisting of solid dots of adhesive, which may or may not be interconnected by thinner intervening filament sections.
Generally, the dispensing of adhesives onto a substrate may be monitored either visually or through the use of various types of conventional infrared and ultraviolet sensors. For example, infrared sensors may be employed for monitoring infrared radiation emitted from adhesive residing on the substrate. As another example, the fluorescence in the visual region of the electromagnetic spectrum from the adhesive residing on the substrate may be monitored when the adhesive is illuminated by ultraviolet radiation.
A persistent problem characterizing the application of a patterned adhesive onto an elastic strand is an inability to determine whether or not the pattern is being properly applied to each elastic strand before the strands are applied to the substrate. Improper application may arise from, for example, excessive movement or motion of the parent machine with which the adhesive dispenser is attached, misalignment of the dispensed adhesive relative to the moving elastic strand, or clogging of one or more of the individual dispenser adhesive discharge outlets or air jets. If improper application is undetected, defective hygienic articles may be produced with a resulting loss of usable product yield.
Conventional methods for monitoring the dispensing of adhesive onto substrates are inadequate for sensing the presence or absence of a pattern applied to an elastic strand. Elastic strands typically have a diameter in the range of about 15 mils to about 20 mils. The addition of the adhesive to the strand increases the effective diameter of the strands. However, a machine operator may not be able to sense the presence or absence of adhesive with the naked eye.
Conventional monitoring techniques lack the sensitivity for accurately determining the presence or absence of adhesive from observation of the strand and adhesive after contact is established with the substrate. Such monitoring techniques, otherwise capable of observing large amounts of adhesive residing on a substrate, are not well suited for monitoring the application of a small-volume pattern of adhesive to a strand. In particular, such techniques are not effective for observing a small-volume pattern of adhesive applied to a strand moving at high line speeds as great as 1200 feet per minute. The adhesive residing on the strand is a small portion of the much larger substrate and, therefore, is difficult to distinguish from the material forming substrate. The substrate and adhesive are also typically formed from similar materials, usually polymeric resins, which increases the difficulty of distinguishing the adhesive from the substrate. Sensors used in conventional monitoring techniques typically monitor an absolute level of adhesive. Generally, such sensors may experience drift during operation that may erroneously indicate a problem with the adhesive dispensing.
Even if the pattern of adhesive is successfully applied to an elastic strand, it is critical in the manufacture of certain hygienic articles to monitor whether or not the applied amount is correct or within an acceptable range. In addition to being securely bonded to the substrate, the elastic strands must also transfer the desired elastic properties to the substrate. If the amount of adhesive on a strand is deficient, the strand may not be adequately bonded to the substrate. If the amount of adhesive on one or more strands exceeds a targeted volume, the adhesive application process loses cost effectiveness since more adhesive is being applied than is required to provide an adequate bond. In addition, the elastic properties of the bonded elastic strand or strands and substrate, such as product flexibility and the formation of rugosities when the stretched strands relax, may be degraded by the presence of excessive adhesive.
For these and other reasons, it would be desirable to provide apparatus and methods for monitoring the application of a viscous material, such as an adhesive, in a pattern to one or more strands.
The invention provides an apparatus for applying an adhesive in a pattern onto a moving strand, or other relatively narrow substrates, for subsequently securing the strand to a substrate. The apparatus includes a coating applicator capable of applying viscous material in a pattern onto the moving strand and a detection unit capable of sensing radiation originating from at least the viscous material. The detection unit is further capable of determining a detected value representative of a characteristic of the pattern from the sensed radiation, comparing the detected value with a reference value representative of a desired standard for the characteristic, and outputting a signal in accordance with the comparison result. The characteristic may be used to determine the presence or absence of the adhesive filament, or may be used to determine whether a proper volume of adhesive is being applied.
In one specific embodiment of the apparatus of the invention, the detection unit is a machine vision system including a camera and a controller. The camera is capable of capturing an image of the strand and viscous material. The controller is capable of determining a detected value representative of a characteristic of the pattern from the image, comparing the detected value with a reference value representative of a desired standard for the characteristic, and outputting a signal in accordance with the comparison result.
According to the principles of the invention, a method is provided for applying a viscous material onto a moving strand for securing the strand to a substrate. The method includes moving the strand in a travel path, applying a viscous material in a pattern onto the moving strand, sensing radiation originating from at least the viscous material, and determining a detected value representative of a characteristic of the pattern from the sensed radiation. The method further includes comparing the detected value with a reference value representative of a desired standard for the characteristic and outputting a signal in accordance with the comparison result.
In one specific embodiment of the method of the invention, the sensing of radiation further comprises capturing an image of the strand, and determining of the detected value further comprises processing the captured image. The image processing may further include determining the volume of adhesive in the pattern, which permits a determination of whether or not a proper amount of adhesive is contained in the adhesive filament being applied to the strand.
According to the principles of the invention, detecting a characteristic of the adhesive pattern, before the strand is applied to a substrate, increases the sensitivity and reliability of adhesive monitoring. In particular, the adhesive filament is easier to perceive before the strand is applied to the much larger substrate. Therefore, the pattern of adhesive may be applied to the moving strand with an improved consistency. In particular, the sensitivity and reliability of the monitoring is significantly improved for strands moving with high speeds. Moreover, the ability to monitor the application of the adhesive pattern reduces waste adhesive arising from improper application and reduces the likelihood of lost usable product yield. The principles of the invention also provide predictive maintenance possibilities.
These and other features, objects and advantages of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description, taken in conjunction with the accompanying drawings.